The present invention relates to heteroaryl compounds that are protein kinase inhibitors, compositions containing such compounds, and methods for their use. The compounds and compositions of the invention are useful for treating cancer, neurological disorders, autoimmune disorders, and other diseases that are alleviated by protein kinase inhibitors.
Mammalian cells respond to extracellular stimuli by activating signaling cascades that are mediated by members of the mitogen-activated protein (MAP) kinase family, which include the extracellular signal regulated kinases (ERKs), the p38 MAP kinases and the c-Jun N-terminal kinases (JNKs). MAP kinases (MAPKs) are activated by a variety of signals including growth factors, cytokines, UV radiation, and stress-inducing agents. MAPKs are serine/threonine kinases and their activation occur by dual phosphorylation of threonine and tyrosine at the Thr-X-Tyr segment in the activation loop. MAPKs phosphorylate various substrates including transcription factors, which in turn regulate the expression of specific sets of genes and thus mediate a specific response to the stimulus.
ERK2 is a widely distributed protein kinase that achieves maximum activity when both Thr183 and Tyr185 are phosphorylated by the upstream MAP kinase, MEK1. Upon activation, ERK2 phosphorylates many regulatory proteins, including the protein kinases Rsk90 and MAPKAP2, and transcription factors such as ATF2, Elk-1, c-Fos, and c-Myc. ERK2 is also a downstream target of the Ras/Raf dependent pathways and relays the signals from these potentially oncogenic proteins. ERK2 has been shown to play a role in the negative growth control of breast cancer cells and hyperexpression of ERK2 in human breast cancer has been reported. Activated ERK2 has also been implicated in the proliferation of endothelin-stimulated airway smooth muscle cells, suggesting a role for this kinase in asthma.
Overexpression of receptor tyrosine kinases such as EGFR and ErbB2, as well as activating mutations in the Ras GTPase proteins or B-Raf mutants are major contributors to human cancer. These genetic alterations are correlated with poor clinical prognosis and result in activation of the Raf-1/2/3-MEK1/2-ERK1/2 signal transduction cascade in a broad panel of human tumors. Activated ERK (i.e., ERK1 and/or ERK2) is a central signaling molecule that has been associated with the control of proliferation, differentiation, anchorage-independent cell survival, and angiogenesis, contributing to a number of processes that are important for the formation and progression of malignant tumors. These data suggest that an ERK1/2 inhibitor will exert pleiotropic activity, including proapoptotic, anti-proliferative, anti-metastatic and anti-angiogenic effects, and offer a therapeutic opportunity against a very broad panel of human tumors.
Many diseases are associated with abnormal cellular responses triggered by protein kinase-mediated events, such as, for example, autoimmune diseases, inflammatory diseases, bone diseases, metabolic diseases, neurological and neurodegenerative diseases, cancer, cardiovascular diseases, allergies and asthma, Alzheimer's disease, and hormone-related diseases. Accordingly, there has been a substantial effort in medicinal chemistry to find protein kinase inhibitors that are effective as therapeutic agents and there is still a need for new therapeutic agents that inhibit these protein targets.